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https://github.com/facebook/react.git
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Mofei Zhang
1fdbcfe162
---
> If this operand is used in a scope, has a dynamic value, and was defined
before this scope, then its a dependency of the scope.
> (from current comments in PropagateScopeDependencies::visitDependency)
A reactive scope can take a dependency from a definition produced by an
incomplete parent scope. Our tests previously did not cover this, since most
object types aliased together and remained mutable throughout a ReactiveScope.
e.g. our tests did not have
```
scope @0 (deps=..., declarations=[x, y]) {
x = {};
// define a reactive, immutable value that is not aliased to become mutable
const immutableVal = ...;
scope @1 (deps=immutableVal, declarations=[y]) {
y = read(immutableVal)
}
mutateX(x, ...);
}
```
We should not add a dependency if it is produced in exactly the same scope as
the one it is used. It is safe (and correct) to depend on values produced by a
parent scope.
---
Note that we still should check for whether a defining scope is active to
determine whether it should be added as a output of that scope
([src](https://github.com/facebook/react-forget/blob/b608ab20d57229b528deeffa19f1ee08a4bad37a/forget/src/ReactiveScopes/PropagateScopeDependencies.ts#L469-L478)).
Access of an identifier produced by a parent scope (i.e. adding a variable
defined by a scope's parent as its own dependency) does not require adding that
identifier to the parent's `declarations`, since that identifier is already
valid to access via identifier binding rules.